Re: length of community strings

[Bart V. A. <bar...@gm...>]

On Wed, Apr 15, 2009 at 8:20 PM, Mike Ayers <mik...@tv...> wrote:
>> From: Dave Shield [mailto:D.T...@li...]
>> The specs implicitly allow an arbitrary length string
>> (although there may be some limit imposed by ASN.1
>> or BER - I'm not sure offhand).
>
>        Over a million octets, IIRC.
>
>> > Is there some defacto standard for maximum length.
>>
>> The main restriction will be from MIB objects that take
>> a community string as their value.
>
>        There's another aspect to take into account.  SNMP is run over UDP in the (vast)
> majority of cases, and therefore all information in a request or response must fit into a
> single UDP packet.  I'd have to consult references for the exact number, but there's
> about 1300+ bytes available for UDP packets over a standard ethernet link.  Since
> you need to put varbinds in the packet, too, the space fills up quickly.

An UDP packet can contain at most 65527 bytes data. UDP packets that
do not fit in a single Ethernet packet (max. 1500 bytes when not using
GbE jumbo frames) get fragmented over multiple Ethernet packets. See
also http://en.wikipedia.org/wiki/User_Datagram_Protocol.

Bart.